Pulsed laser induced plasma and thermal effects on molybdenum carbide for dry reforming of methane

Dry reforming of methane (DRM) is a highly endothermic process, with its development hindered by the harsh thermocatalytic conditions required. We propose an innovative DRM approach utilizing a 16 W pulsed laser in combination with a cost-effective Mo2C catalyst, enabling DRM under milder conditions. The pulsed laser serves a dual function by inducing localized high temperatures and generating *CH plasma on the Mo2C surface. This activates CH4 and CO2, significantly accelerating the DRM reaction. Notably, the laser directly generates *CH plasma from CH4 through thermionic emission and cascade ionization, bypassing the traditional step-by-step dehydrogenation process and eliminating the rate-limiting step of methane cracking. This method maintains a carbon-oxygen balanced environment, thus preventing the deactivation of the Mo2C catalyst due to CO2 oxidation. The laser-catalytic DRM achieves high yields of H2 (14300.8 mmol h−1 g−1) and CO (14949.9 mmol h−1 g−1) with satisfactory energy efficiency (0.98 mmol kJ−1), providing a promising alternative for high-energy-consuming catalytic systems.


The photothermal catalytic performance test in the closed batch system
By placing the Mo2C NSs (20 mg) on quartz cotton at the bottom of the quartz reactor, the mixed gas of CO2, CH4 and Ar at a ratio of 47.5%:47.5%:5%was poured into the reactor for 15 mins to remove air in the reactor, then closed the reactor vent.The light intensity of a 300 W Xe lamp with a plano-convex lens is 3 W cm -2 .The post-reaction gases were analyzed using a GC to obtain the relative amounts of CO, H2, CO2, and CH4.

Quantification of reaction yields, selectivity, conversion, and energy efficiency
The reaction yields were calculated based on the mass of the Mo2C: The selectivity is expressed as the ratio of H2 to CO produced: The conversion of reactant was calculated using: The total energy efficiency of laser-catalysis and thermocatalysis was calculated using: The total energy efficiency of photocatalysis was calculated using: The electricity cost of laser-catalysis, thermocatalysis, and photocatalysis was calculated using: C= ∆ p refers to the percentage change of a product in the reactor; Fin and Fout refer to the reaction gas flow rate of inlet and outlet, respectively; r CH 4 ,converted and r CO 2 ,converted refer to rate of conversion of CH4 and CO2 (mmol s -1 ), respectively; P output refers to the output power of the pulsed laser (16 W) and the fixed-bed reactor (496 W); P L refers to the luminous power of the Hg-Xe lamp (60 W, output power of the 150 W Hg-Xe lamp); P E refers to the electric power of the pulsed laser (1200 W), the fixed-bed reactor (730 W), and the Hg-Xe lamp (150 W).

COMSOL theory simulations
In addition to the experimental study, the laser heating of Mo2C/BaSO4 tablet and the laser induced plasma of the mixed gas were theoretically simulated.The calculations were carried out in COMSOL Multiphysics® and the physical models used in the simulation modeling process included: unipolar ion drift model, reduced drift-diffusion model, complex chemistry kinetic model.The specific parameters of the modeling process were as follows: laser output power 16 W, laser spot radius 50 μm, laser pulse period 20 kHz, pulse width 100 ns.

1 .
13) CO2 atmosphere, two additional peaks at 40.52° and 58.61°, corresponding to (200), (220) crystal planes of Mo appeared.Under pure CH4 atmosphere, the C* produced by methane cracking resulted in the formation of Mo0.42C0.58 with characteristic diffraction peaks at 37.07 o and 42.83°.While under CO2: CH4 feed ratio of 1:1 atmosphere, Mo2C phase remained intact, suggesting that the equilibrium reaction between CH4 and CO2 occurred.According to previous research, the O* produced by the reduction of CO2 and the C* produced by the cracking of CH4 further reacted to form CO under the catalysis of Mo2C Supplementary Figure 14.HRTEM image of Mo2C using FIB pick-up system from the laser irradiated areas.

Table S3 . Catalytic performance of the samples calculated from effective Mo2C mass within laser irradiation area.
Effective Mo2C Mass is defined as the amount of Mo2C covered within a laser irradiation area of 0.69 mm 2 .